[PULL for-4.2 2/3] net/virtio: Fix failover error handling crash bugs

[Markus Armbruster <armbru@redhat.com>]

Functions that take an Error ** parameter to pass an error to the
caller expect the parameter to point to null.
failover_replug_primary() violates this precondition in several
places:

* After qemu_opts_from_qdict() failed, *errp is no longer null.
  Passing it to error_setg() is wrong, and will trip the assertion in
  error_setv().  Messed up in commit 150ab54aa6 "net/virtio: fix
  re-plugging of primary device".  Simply drop the error_setg().

* Passing @errp to qemu_opt_set_bool(), hotplug_handler_pre_plug(),
  and hotplug_handler_plug() is wrong.  If one of the first two fails,
  *errp is no longer null.  Risks tripping the same assertion.
  Moreover, continuing after such errors is unsafe.  Messed up in
  commit 9711cd0dfc "net/virtio: add failover support".  Fix by
  handling each error properly.

failover_replug_primary() crashes when passed a null @errp.  Also
messed up in commit 9711cd0dfc.  This bug can't bite as no caller
actually passes null.  Fix it anyway.

Fixes: 9711cd0dfc3fa414f7f64935713c07134ae67971
Fixes: 150ab54aa6934583180f88a2bd540bc6fc4fbff3
Cc: Jens Freimann <jfreimann@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20191130194240.10517-3-armbru@redhat.com>
Reviewed-by: Jens Freimann <jfreimann@redhat.com>
---
 hw/net/virtio-net.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 87088ba374..db3d7c38e6 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -2795,6 +2795,7 @@ static bool failover_unplug_primary(VirtIONet *n)
 
 static bool failover_replug_primary(VirtIONet *n, Error **errp)
 {
+    Error *err = NULL;
     HotplugHandler *hotplug_ctrl;
     PCIDevice *pdev = PCI_DEVICE(n->primary_dev);
 
@@ -2806,27 +2807,33 @@ static bool failover_replug_primary(VirtIONet *n, Error **errp)
                 qemu_find_opts("device"),
                 n->primary_device_dict, errp);
         if (!n->primary_device_opts) {
-            error_setg(errp, "virtio_net: couldn't find primary device opts");
-            goto out;
+            return false;
         }
     }
     n->primary_bus = n->primary_dev->parent_bus;
     if (!n->primary_bus) {
         error_setg(errp, "virtio_net: couldn't find primary bus");
-        goto out;
+        return false;
     }
     qdev_set_parent_bus(n->primary_dev, n->primary_bus);
     n->primary_should_be_hidden = false;
     qemu_opt_set_bool(n->primary_device_opts,
-                      "partially_hotplugged", true, errp);
+                      "partially_hotplugged", true, &err);
+    if (err) {
+        goto out;
+    }
     hotplug_ctrl = qdev_get_hotplug_handler(n->primary_dev);
     if (hotplug_ctrl) {
-        hotplug_handler_pre_plug(hotplug_ctrl, n->primary_dev, errp);
+        hotplug_handler_pre_plug(hotplug_ctrl, n->primary_dev, &err);
+        if (err) {
+            goto out;
+        }
         hotplug_handler_plug(hotplug_ctrl, n->primary_dev, errp);
     }
 
 out:
-    return *errp == NULL;
+    error_propagate(errp, err);
+    return !err;
 }
 
 static void virtio_net_handle_migration_primary(VirtIONet *n,
-- 
2.21.0